When power transmission and interruption between an inner ring and an outer ring are to be repeated, a one-way clutch is usually placed between the inner and outer rings.
FIG. 6(A) is a partial section view of a one-way clutch configured by a cage 3, a spring (ribbon spring) 16, and sprags 5 serving as engagement members, and FIG. 6(B) is an enlarged view of portion R in FIG. 6(A). In the one-way clutch, in order to enable the cage 3 to synchronize with the rotation of the outer ring, it is common to employ a configuration where a flange portion which is not illustrated, and which radially extends is disposed in, for example, an end portion of the cage 3 to provide a fastening zone, and the cage is pressingly inserted into the outer ring 1. One or two cages 3 (an outer cage and an inner cage) are used. In any case, the engagement members 5 (hereinafter, referred to as sprags 5) are placed in pocket 16p which are disposed on the spring 16 circumferentially at regular intervals, and urged in the engagement direction (wedge function direction) by tongues 16c disposed in the spring 16.
FIG. 7 is a partial perspective view of the spring 16, FIG. 8(A) is a plan view which is developed in the circumference direction of the spring 16, and FIG. 8(B) is a section view taken along the line A-A of FIG. 8(A) and a partial section view showing a state where the spring is actually placed in a one-way clutch (the sprags 5 are not placed).
In the spring 16, a thin metal plate member (for example, stainless steel), and bases 16a, 16a which are annular when incorporated, columns 16b, 16b, . . . which connect the base 16a and the base 16a, pockets 16p, 16p, . . . which are formed between the base 16a, 16a, . . . and the columns 16b and disposed circumferentially at regular intervals, and tongues 16c, 16c, . . . which elongate from center portions of the columns 16b toward the pockets are formed by press working. In this case, the configuration where the tongues 16c have tongues 16c which are previously inward bent before the spring 16 is placed in an annular space 4 has been conventionally known (see Japanese Utility Model Application (Kokai) No. HEI2-76234).
In each of the tongues 16c, three meandering bends (16d, 16e, 16f) are formed from a basal end portion of the column 16d. In such a case, usually, it is most frequent that, as shown in FIG. 9, the height d2 of a tip end portion of the tongue 16c to the base 16a is smaller than the height d1 of the second meandering bend 16e to the base 16a, and, in a state where the sprag 5 is urged, the height d2 of the tip end portion of the tongue 16c to the base 16a is larger than d1.
In a one-way clutch, a drag torque (friction torque) is inevitably generated in power transmission and interruption between inner and outer rings. In a one-way clutch, the drag torque depends on a spring force (spring constant) of a tongue of a spring which urges a sprag in the engagement direction. Specifically, when an urging force of a tongue is made large (a spring constant is made large), the engagement property of a sprag is good, but the drag torque is large. By contrast, when the urging force of the tongue is excessively small, the engagement property of the sprag is impaired, and an engagement failure occurs. Therefore, a one-way clutch in which a drag torque is made as small as possible while maintaining the engagement property is requested. Recently, from the viewpoint of energy saving, friction loss must be reduced, and, also in a sprag type one-way clutch, a drag torque must be reduced as far as possible. In a one-way clutch for a torque converter or the like, disengage type sprags are used, but reduction of a drag torque in a low rotation zone is not sufficient.
The invention has been conducted in order to cope with the above-discussed problems. It is an object of the invention to provide a one-way clutch spring which has a high engagement property, and in which a drag torque (friction torque) is considerably lower than the conventional one.